In keeping with an increasing environmental consciousness cooling medium compressors which operate with environmentally friendly cooling mediums are achieving an always greater significance. Especially, one is prompted to avoid cooling mediums which stand in suspicion of creating a hothouse effect.
Therefore, increasingly cooling mediums are used which have hydrocarbon bases, for example a cooling medium R600 (isobutane). Such cooling mediums are today heavily used in Europe and a number of cooling furniture pieces offered on the European market are operated with cooling medium R600.
Some of the environmentally friendly cooling mediums have above all the disadvantage that they are easily ignitable. This leads in connection with further development of cooling medium compressors to the following problem: on energy saving grounds increasingly compressors are used whose rotational speeds are variable. Such compressors are electronically controlled. Possibly this control among other things includes the use of new motor technologies, for example permanent magnet excited motors or one, two, or three phase induction motors.
Such compressors, or more correctly said their drive motors, are not only switched on and off, but are much more controlled by way of power semiconductors. In connection with this control a situation can arise by way of which an ignitable gas mixture can become ignited.
If therefore two fault possibilities appear at the same time, namely first a leak in the cooling system through which the cooling medium can escape, and secondly a fault in the electronic control, an ignition of the cooling medium gases can occur. If this ignition occurs suddenly, it can indeed produce small explosions.
Therefore, in JP 8-247 646 A it is proposed that a gas sensor be arranged in the cooling space and that an electrical supply be interrupted if the sensor determines the presence of gas. In this case it is necessary to provide an electrical conductor between the gas sensor and the control mechanism to connect the gas sensor from the interior of the cooling cabinet with the control mechanism.
Along with this there are further possibilities for solving this problem, which are briefly set forth as follows:
One can provide a fuse, that is a glass fuse, in a power supply phase. This is today a very widely used solution. The glass fuse is, however, typically relatively unreliable and in the manufacturing of the compressor is difficult to manage.
One can hermetically seal the housing of the control mechanism so that the cooling medium gas in the case of a leak in the cooling arrangement cannot penetrate to the components of the control mechanism. The sealing of the housing is, however, difficult. It leads moreover in many cases to thermal problems in the control mechanism.
One can diminish the free volume in the housing of the control mechanism so far that it is smaller than 20 cm3. This is the limiting value of a safety standard. This can be achieved for example, by the moulding of a filling or potting material into the housing in which the control mechanism is contained. Above all, this solution is relatively expensive and mechanically loads the components of the control mechanism, especially by material movement with increased temperatures.
The invention has as its object the improvement of safety in cooling medium compressor arrangements.